The present invention relates to an image recording apparatus which employs an elongated photosensitive image recording medium. More particularly, the invention relates to such image recording apparatus having a sheet slack absorbing roller and a driving mechanism therefor.
In one type of a conventional image recording apparatus, a dancer roller is provided for absorbing a sheet slack which may be provided in the image recording operation. Further, the photosensitive image recording medium includes a microcapsule sheet in which microcapsules encapsulating therein chromogenic materials are coated on a substrate. In the conventional apparatus, an outer peripheral surface of the dancer roller is not in contact with the microcapsule layer but is in contact with the substrate surface. Therefore, no contamination occurs in the roller surface due to the transfer of the chromogenic materials from the ruptured microcapsules. In other words, since no deposition of the chromogenic materials occurs at the outer surface of the dancer roller, the microcapsules coated on the microcapsule sheet substrate can be protected against any damage.
However, when taking an entire microcapsule sheet path into consideration, another spacial problem arises such as minimization of the sheet path length, and layout of entire components of the recording apparatus, yet providing large motion of the dancer roller for absorbing great amount of the sheet slack. Consequently, there has been provided an another type of an image recording apparatus in which the microcapsule layer is in contact with the surface of the dancer roller.
As is well known in the art, the microcapsules are photo-cured upon light exposure, and therefore, the photo-cured portions is not ruptured. However, if unexposed area of the microcapsule sheet where no latent image is formed thereon is in contact with the dancer roller surface or nip rollers or feed rollers, the unexposed microcapsules are easily ruptured on these roller surfaces. Such ruptured portions may degrade quality of the output image.
Further, in the image recording operation, the unexposed microcapsule sheet zone may be moved to the immediately upstream side of the pressure developing roller for performing the pressure developing operation with respect to the light exposed zone of the microcapsule sheet forming a latent image thereon. In this case, in order to save cost, the unexposed zone of the microcapsule sheet is reversely fed toward an exposure table for a next exposure operation against the unexposed zone. However, the unexposed area of the microcapsule sheet is in contact with the dancer roller, so that the unexposed microcapsules may be ruptured. Moreover, during non operative state of the image recording apparatus or standby state thereof, if the microcapsule layer is continuously contacted with the dancer roller surface, the dancer roller surface may be contaminated with the materials of the microcapsules.
In another aspect of this art, when a new microcapsule sheet is intended to be installed in the image recording apparatus, a leader tape portion of the microcapsule sheet must pass through the microcapsule sheet path. For correctly directing the leader tape portion along the sheet path in order to install the microcapsule sheet at the sheet path, conventionally, guide members are provided at a space between rollers such as feed rollers. The guide members are formed of iron or resin plate. However, if the guide member has an enlarged area, its mechanical strength may be lowered, and deformation may occur. If the guide member is deformed, the microcapsule sheet path may be deviated. Further, if the guide members are juxtaposedly provided along the sheet path with a narrow distance, the deformation of the guide plates may affect the travel of the leader portion, and further, it would be rather troublesome for assembling such guide plates in the limited space of the image recording apparatus. If the guide member is excessively deformed, the subsequent microcapsule sheet may contact with the guide plate surface, which in turn damages to the surface of the microcapsule sheet, and sheet wrinkle may occur. Furthermore, after the leader tape portion reaches the takeup shaft and is correctly wound thereover, the guide member for guiding the leader tape portion is not any more required. Moreover, if the dancer roller is positioned at the sheet path, the leader portion may abut the dancer roller, and therefore, the leader portion cannot reach the takeup shaft. And if the dancer roller is positioned above the sheet path at the time of sheet loading, the sheet slack absorbing function may not be achievable after the microcapsule sheet is installed at the sheet path.
In still another aspect, the conventional dancer roller is linearly movable by making use of its own weight so as to provide the sheet slack absorbing function. This linear movement is only available in a case where small sheet slack amount is provided. However, in an attempt to carry out large sheet slack absorbing function, the linear moving stroke must be large, and therefore, large space must be required for allowing the dancer roller to be movable by a large distance. Hence, a mechanism for linearly moving the dancer roller by a large distance may become complicated.